A full-dimensional quantum dynamical study of H2+H2 collisions: Coupled-states versus close-coupling formulation

Abstract

Collision-induced energy transfer involving H2 molecules plays an important role in many areas of physics. Kinetic models often require a complete set of state-to-state rate coefficients for H2+H2 collisions in order to interpret results from spectroscopic observations or to make quantitative predictions. Recent progress in full-dimensional quantum dynamics using the numerically exact close-coupling (CC) formulation has provided good agreement with existing experimental data for low-lying states of H2 and increased the number of state-to-state cross sections that may be reliably determined over a broad range of energies. Nevertheless, there exist many possible initial states (e.g., states with high rotational excitation) that still remain elusive from a computational standpoint even at relatively low collision energies. In these cases, the coupled-states (CS) approximation offers an alternative full-dimensional formulation. We assess the accuracy of the CS approximation for H2+H2 collisions by comparison with benchmark results obtained using the CC formulation. The results are used to provide insight into the orientation effects of the various internal energy transfer mechanisms. A statistical CS approximation is also investigated and cross sections are reported for transitions which would otherwise be impractical to compute.

Universal few-body physics and cluster formation

“…A handful of studies have even gone beyond three-atom processes and computed scattering cross sections for reactions involving four-atoms using hyperspherical (Clary, 1991) or other methods (Bohr et al, 2014). These studies can be viewed as solutions to the few-body Schrödinger equation, starting from the Born-Oppenheimer potential energy surface as a function of the internuclear coordinates.…”

Mutual vibrational quenching in CO + H2 collisions

“…Based on the comparisons and previous experience with H 2 -H 2 30 , we conservatively estimate that the results are reliable to within 50% for most transitions and give the correct trends in the relative cross sections. A full database of such cross sections and associated rate coefficients would add to existing rotational quenching data 38 and provide an invaluable tool for astrophysical models.…”

“…The CC and CS formulations have both been developed for diatom-diatom systems [27][28][29] and a comparison of the two formulations was recently given for H 2 +H 2 in full dimensionality 30 . In the present work, we investigate the possibility of using the CS approximation to describe the dynamics of CO+H 2 collisions.…”

STATE-SPECIFIC DISSOCIATION RATES FOR H2(v, j) + H2(v′, j′)

“…The determination of state-specific H 2 +H 2 rate coefficients requires a significant computational effort (Mandy & Pogrebnya 2004;Bohr et al 2014) and it would be prudent to explore how necessary are these computationally costly rate coefficients. This may be explored further through model kinetic master equation calculations (cf.…”